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Fair value - pension and postretirement (Details 9) (USD $) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Pension Benefits |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | $ 334,844,000 |  | $ 309,184,000 |  | $ 278,000,000
Percentage investment in common stock of large-cap U.S. companies | 34.00% |  | 26.00% |  |
Percentage investment in US Treasuries | 11.00% |  | 13.00% |  |
Percentage investment in common stock of mid-cap U.S. companies | 11.00% |  | 12.00% |  |
Percentage investment in corporate bonds | 27.00% |  | 41.00% |  |
Percentage investment in other investments | 17.00% |  | 8.00% |  |
Estimated future employer contributions in next fiscal year | 32,500,000 |  |  |  |
Pension Benefits | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 9,406,000 |  | 12,605,000 |  |
Pension Benefits | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 62,599,000 |  | 86,981,000 |  |
Pension Benefits | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 39,437,000 |  | 39,818,000 |  |
Pension Benefits | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 158,748,000 | [1] | 102,852,000 | [2] |
Pension Benefits | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 42,721,000 |  | 45,112,000 |  |
Pension Benefits | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 7,561,000 |  | 9,302,000 |  |
Pension Benefits | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 11,822,000 |  | 12,514,000 |  |
Pension Benefits | Total assets measured at fair value [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 332,294,000 |  | 309,184,000 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 2,145,000 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 62,599,000 |  | 86,981,000 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 39,437,000 |  | 39,818,000 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 116,265,000 | [1] | 82,787,000 | [2] |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 7,487,000 |  | 7,980,000 |  |
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Total assets measured at fair value [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 225,788,000 |  | 219,711,000 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 9,406,000 |  | 10,460,000 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 42,483,000 | [1] | 20,065,000 | [2] |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 42,721,000 |  | 45,112,000 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 7,561,000 |  | 9,302,000 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 4,335,000 |  | 4,534,000 |  |
Pension Benefits | Significant Other Observable Inputs (Level 2) | Total assets measured at fair value [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 106,506,000 |  | 89,473,000 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 | [1] | 0 | [2] |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Pension Benefits | Significant Unobservable Inputs (Level 3) | Total assets measured at fair value [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 84,543,000 |  | 74,361,000 |  | 68,085,000
Percentage investment in common stock of large-cap U.S. companies | 55.00% |  | 51.00% |  |
Percentage investment in US Treasuries | 12.00% |  | 15.00% |  |
Percentage investment in mortgage backed securities | 8.00% |  | 10.00% |  |
Percentage investment in common stock of mid-cap U.S. companies | 8.00% |  |  |  |
Percentage investment in corporate bonds | 9.00% |  | 11.00% |  |
Percentage investment in other investments | 8.00% |  | 13.00% |  |
Estimated future employer contributions in next fiscal year | 1,500,000 |  |  |  |
Other Postretirement Benefits | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 2,142,000 |  | 3,044,000 |  |
Other Postretirement Benefits | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 2,802,000 |  | 2,207,000 |  |
Other Postretirement Benefits | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 221,000 |  | 260,000 |  |
Other Postretirement Benefits | Insurance investment contract [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 79,374,000 | [3] | 68,850,000 | [4] |
Other Postretirement Benefits | Total assets measured at fair value [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 84,539,000 |  | 74,361,000 |  |
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 3,023,000 |  | 3,520,000 |  |
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 1,053,000 |  |
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 2,802,000 |  | 2,207,000 |  |
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 221,000 |  | 260,000 |  |
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1) | Insurance investment contract [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 | [3] | 0 | [4] |
Other Postretirement Benefits | Significant Other Observable Inputs (Level 2) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 81,516,000 |  | 70,841,000 |  |
Other Postretirement Benefits | Significant Other Observable Inputs (Level 2) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 2,142,000 |  | 1,991,000 |  |
Other Postretirement Benefits | Significant Other Observable Inputs (Level 2) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Other Observable Inputs (Level 2) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Other Observable Inputs (Level 2) | Insurance investment contract [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 79,374,000 | [3] | 68,850,000 | [4] |
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3) | Insurance investment contract [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | $ 0 | [3] | $ 0 | [4] |
[1] | Collective and mutual funds invest approximately 11 percent in common stock of mid-cap U.S. companies, 34 percent in common stock of large-cap U.S. companies, 11 percent in U.S. Treasuries, 27 percent in corporate bonds and 17 percent in other investments.
[2] | Collective and mutual funds invest approximately 12 percent in common stock of mid-cap U.S. companies, 26 percent in common stock of large-cap U.S. companies, 13 percent in U.S. Treasuries, 41 percent in corporate bonds and 8 percent in other investments.
[3] | The insurance contract invests approximately 55 percent in common stock of large-cap U.S. companies, 12 percent in U.S. Treasuries, 8 percent in mortgage-backed securities, 8 percent in common stock of mid-cap U.S. companies, 9 percent in corporate bonds and 8 percent in other investments.
[4] | The insurance contract invests approximately 51 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Treasuries, 10 percent in mortgage-backed securities, 11 percent in corporate bonds and 13 percent in other investments.

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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930 + Details
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